I promised I wouldn't force a monthly fee on the players, but I didn't say anything about players paying for additional services.
And no this is nothing like 'premium' service.
The game would include a world editor. (which can only edit terrain and structures. There's a reason for this)
Players can rent their own little world using server space owned by the game. What I would like to do is leave the price open-ended (with a minimum of say...$5 a month) so people could if they want make a world with complexities ranging from just a small town to a fully fleshed out discworld.
In terms of ability to pay, they can reduce the amount they pay, but there's a direct relation between how much is paid and how much server space is allotted to them. (The edges of the rented space would be covered in impassible fog, kinda like Zelda LttP) So when they reduce their payment, the fog closes in on their space. Any losses are stored for a billing cycle or three before deletion depending on the record of the creator.
These worlds follow the same engines and systems as Hub, but are actually separate from it. People would have to 'mirror' to their world to get there. Creators can even set a password for entering their world.
Creators are NOT allowed to just create items. All to often this would lead to effective 'black market' items where creators make items and either just give them away or sell them for profit. They CAN design items and submit them for inclusion into the next update. (if accepted in most cases they'll end up being given it by the admin)